Despite this, there are concerns that the virus that causes smallpox could be used as a bioweapon, the FDA said.

“To address the risk of bioterrorism, Congress has taken steps to enable the development and approval of countermeasures to thwart pathogens that could be employed as weapons,” Dr. Scott Gottlieb, the FDA commissioner, said in a statement.

Smallpox has not technically been wiped off the planet as some stocks of the virus still exist in labs in the United States and in Russia.

But some governments believe there is a risk that the virus exists in other places other than these laboratories and could be deliberately released to cause harm, according to the according to the World Health Organization (WHO).

“More animals treated with TPOXX lived compared to the animals treated with placebo,” the FDA said in the statement.

Tpoxx was approved under the FDA’s Animal Rule, which allows animal studies to be used to support approval when it is not feasible or ethical to conduct studies of the drug’s effectiveness in people. However, the drug was tested for safety in more than 350 healthy people who did not have smallpox.